The invention relates to a method for anaerobic digestion of sludge from the treatment of sewage effluents, an anaerobic digester of primary sludge containing effluents, as well as treatment plant comprising mainly such a digester.
Anaerobic digestion of sludge from the treatment of sewage effluents, for example household effluents, consists of hydrolysis and methane fermentation with considerable cell-destroying power, such as to be able to eliminate a considerable amount of the organic material contained in this sludge.
The sludge results, for example, from the settling of raw sewage. At the outlet of the digester, digested sludge is obtained on the one hand, together with effluents on the other, these two parts can then be separately subjected to a number of additional treatments.
Document U.S. Pat. No. 6,673,243 presents an anaerobic sludge digester comprising a tank divided into several successive compartments by means of transversal walls that do not reach the top of the tank. In the first upstream compartment, at the bottom, the sludge to be treated is inserted through a feeding pipe, the treated effluents being drained off from the final downstream compartment through a discharge pipe.
The median transversal wall comprises an opening at the bottom that allows the sludge and effluents to pass from the upstream compartment to the downstream compartment it defines.
On the other hand, none of the other transversal walls have a bottom opening. It follows that, on the one hand, the flow of the effluents alternates between rising and falling and, on the other hand, the sludge can build up in a compartment but cannot flow downstream after being digested. The effectiveness of the digester is therefore considerable diminished.
The invention aims to solve these problems.